Red Wine

Alcohol: high alcohol consumption results in a higher blood pressure and may cause hypertension. It has a positive correlation with mouth- throat- and gullet (med. oesophagus) cancer; under certain circumstances with liver cancer and liver cirrhosis. But what is "high" or "too much"? This definition depends on the country you live in as well as you physiological condition. E.g. in the northern European countries, 2-3 glasses a day is considered more than enough, whereas the Mediterraneans think 5 glasses is still acceptable. Differences on a physiological basis: your body weight, dayly energy intake and the presence of ADH (= alcohol dehydrogenase, an enzyme in the stomach that degrades the alcohol before it can enter the blood stream).

Tannin: these compounds are plant polyphenols and may cause headaches. Tannins tend to bind starches while being digested. These starches are needed by the body to produce serotonin. In some people, who are extremely sensitive to their serotonin levels, it appears the lack of serotonin can lead to a migraine. It sort of "starves" the body for this type of raw material, much as not eating for many hours might lead this person to have the same migraine. Tannin sensitivity is also now thought to be cumulative - a person who begins life with no tannin sensitivities may yet develop one as he or she ages. People who are sensitive to tannins need to moderate their intake of tannins in all forms, and also be sure to eat a reasonable amount of food while ingesting tannins, so the binding affects of tannins do not cause undue stress.
But see also below at the positive aspects.

Sulfites: some people are sensitive to it.

That for the negative aspects, now the more favourable and pleasurable facts of red wine

Positive aspects

Reducing coronary heart diseases: the wine is altering the blood lipid levels. It lowers the total cholesterol count, and raises the high density lipoprotein (HDL) levels. This is supported by epidemiological studies: the polyphenols may be involved in this cardioprotective effect because of their antioxidant and free radical scavenging properties, resulting in decreased generation of oxidized lipids. The tested red wine extracts (cabernet-sauvignon grape variety) elicited enhanced NO generation, cyclic GMP accumulation and endothelium-dependent relaxation in rat aortic rings. Both anthocyanins and oligomeric condensed tannins appeared to be involved. Among the anthocyanins, delphinidin, but not malvidin or cyanidin, produced endothelial NO-dependent vasorelaxation (aka: it smooths the muscles of the blood vessels), indicating that only some specific structures are able to cause endothelium-dependent vasorelaxation, independently of their antioxidant properties. To achieve this effect, extracellular Ca2+ (=calcium ion) is needed for activation (of endothelial NO synthase activation). Summarizing: their findings suggest that one of the mechanisms of the cardioprotective effects of red wine and other plants containing polyphenols may be the increase in endothelial NO production induced by oligomeric condensed tannins and anthocyanins.

Red wine maintains the immune system: According to a study published by the University of Florida, red wine does not suppress the immune system like other alcoholic beverages. A two month study on mice has been performed to examine what immune system reactions red wine caused on mammals. The team examined mice of various drinking levels - non-drinkers, red wine drinkers, and heavy alcohol drinkers. They found that those who drank the red wine had a normal level of immunity, the same as that of the non-drinking mice. (The level of red wine consumption for the mice would equal that of a human drinking two or three glasses a night. But at the moment of writing (2001) they don't have a clue which compounds in red wine is causing this, but I'd go for the tannins.

Polyphenols in wine: like the tannin mentioned above, do have a positive effect on your body as well: they are excellent antioxidants. In short: they lower total cholesterol and blood pressure, lessen risks of cancer, stimulate the immune system, and have anti-bacterial properties. See the above mentioned aspects for more detail.

Resveratrol (trans-3,5,4'-trihydroxystilbene): is a naturally occurring antioxidant too that decreases the stickiness of blood platelets and helps blood vessels remain open and flexible. It is said that it inhibits the enzymes that can stimulate cancer-cell growth and suppress immune response. A series of laboratory experiments suggests the proof of this statement. However, this was only tested on animals. In another set of animal tests, resveratrol was shown to inhibit both the acute and chronic phases of inflammation (yet again the immune system). Wine is the primary dietary source of resveratrol, and red wine contains much greater amounts of resveratrol than does white wine, since resveratrol is concentrated in the grape skin and the manufacturing process of red wine includes prolonged contact with grape skins. Resveratrol has been used in connection with atherosclerosis too (a reduced risk of course).
Resveratrol is a phytoestrogen (= similar to estrogen, but from plant origin, and is known to inhibit tumors in the breast and uterus), but it differs from other phytoestrogens in that it acts as an estrogen agonist and stimulates ERE-driven reporter gene activity in CHO-K1 cells (I couldn't get access to ERE gene information, nor the exact description of CHO-K1 cells, but the context of the abstract implies increased DNA transcription activity of specific ERE-gene sequences in genetically modified(?) cells in rat uteri).
A brief calculation: a glass of red wine provides approximately 640 mcg of resveratrol, while a handful of peanuts provides about 73 mcg. The amount used in animals to prevent cancer, however, would exceed 500 mg per human adult. This equals about 2.5 bottles of wine... So there must be at least one other component, or a mixture, that contributes to the decrease in occurrence of cancer and high blood pressure prevention.

Flavonoids: Red grapes contain flavonoids, also powerful antioxidants that work as cancer preventives.

Anti-bacterial activity: In a study of 1800 people, scientists tested for the presence of Helicobacter pylori, which causes ulcer infections. Compared to non-drinkers, those who had one glass of wine a day had 7% fewer of these bacteria. Those who drink two glasses a day had 18%, and those who drank 3 or more glasses had 1/3 fewer bacteria. On the conto of tannins maybe?

Anti-stress: wine does have a calming influence (surprise, surprise). The fact that a dinner is accompanied by a drink which helps the body relax and unwind can help the mental transition between work and relaxation. Also, people fighting other illnesses can combat them better when calm and focused.

However, remains the question for the Health Board and researchers to clarify if red grape juice is as healthy as red wine. I'm not aware of published results that prove this hypothesis. During my study at the university some research has been carried out, of which the results show that the grape juice does have some positive effects, but not as profound as red wine. hihaa! Really, this is not just my selective memory speaking. During the preliminary research they didn't have the faintest idea for constructing a nice and plausible explanation for that, other then the scientifically correct description that goes something like this: "it is very likely a combination of well balanced different components and possibly environmental parameters acting together that influences the overall beneficial effect of red wine".

Conclusion

The net effect of drinking at least 2 to 3 glasses of wine a day is supposed to result in a healthier life.

Besides my own knowledge, I used the following sources trying to get the results of the most recent research:
http://www.pulsus.com/europe/05_01/stoc_ed.htm
http://endo.edoc.com/end/v141n10/3657-abs-frame.html (is an abstract from Endocrinology, October 2000, Vol. 141, No. 10, pp. 3657-3667)
http://wine.about.com/food/wine/library/encyc/bl_tannin.htm
http://www.healthwell.com/healthnotes/Supp/Resveratrol.cfm